Method and arrangement for optically stimulating the visual system

ABSTRACT

The invention relates to a method and arrangement for optically stimulating the visual system according to the requirements of the static perimetry and for objectively evaluating adequate stimulus-related electrophysical and/or magnetophysical quantities. Physiologically adequate luminous excitations with defined luminous parameters derived from a predetermined correlation function and from the known intensity dependence of the excitation response amplitude are presented to the observer. The excitation responses contained in the ERG and/or in the EEG/MEG are detected and processed. These excitation responses are used to determine and topographically evaluate the local sensitivity of the visual system. In one embodiment, the light sources are fixed inside a perimeter ( 1 ), and the excitation responses are amplified and digitized by a device ( 3 ), which preferably comprises an ERG/EEG measuring system and an A/D converter. To this end, the device ( 3 ), for the purpose of evaluating, and the light sources, for the purpose of controlling, are connected to a controlling means ( 2 ), preferably to a PC provided with evaluation and control software.

FIELD OF THE INVENTION

[0001] The invention refers to a method and an apparatus for optically stimulating the visual system in accordance with the requirements of static perimeters, and for the objective evaluation of adequate stimulus-related electro- and/or magnetophysiological values.

PRIOR ART

[0002] Prior art stimulation systems of objective perimeters that use binary controlled light stimulators are known. To give an example, monofocal light markers of a defined intensity that light up briefly are used in perimeters in order to check the functionality of the visual system.

[0003] In newer systems, multifocal (i.e. simultaneous at more than one location) optical stimuli are used where the sequence of such stimuli is generally controlled by pseudo-random binary sequences usually referred to as m-sequences, MLS (Maximum Length Sequence) or PRBS (Pseudo Random Binary Sequence).

[0004] The disadvantage of the methods used so far is that the generated optical stimuli (whether they were generated mono- or multifocally) have a constant level of intensity during an examination.

[0005] Even though the m-sequences used that are shown individually (monofocally) appear as a random sequence to the subject, the subject's visual system recognizes the basic cycle (the time basis for the change of pattern) very quickly if they are shown simultaneously (multifocally). The recognition of a pattern in the stimulation method automatically leads to a the adaptation of the sensory system to this stimulus, which leads to a decrease in attention. This significantly decreases the measurable evidentiary power of the physiological values examined.

[0006] With such a stimulation modus, only absolute scotoma (complete local failure of the visual function) and a small degree of strong relative scotoma (partial local failure of the visual function, decreased sensitivity) can be diagnosed reliably.

[0007] In order to objectively answer the question regarding the perception of a light impulse at a particular retinal location, the EEG of the subject is analyzed and searched for the presence of a response to the impulse using objective criteria. This creates an objective topological examination result regarding the visual function—but only for one level of intensity of the light impulses.

[0008] For the much more commonly occurring relative scotomas it is necessary to use several logarithmically graduated levels of light in order to topographically record locally occurring losses of sensitivity such as is commonly done in static perimeters.

[0009] Using conventional stimulation methods, the objectification of the static perimeter would result in an unacceptable lengthening of the examination time.

DESCRIPTION OF THE INVENTION

[0010] Progressing on from this prior art, the object of the invention is to identify a method that will make it possible to generate optimized optical impulses with respect to the signal theory that are adequate for the physiological sensory perception, and then check the perception function using electro- and/or magnetophysiological values.

[0011] According to the invention, the object is met by using graduated light intensities in order to stimulate the visual system optically and by determining the chronological sequence and the spatial pattern of the light impulses with respect to an objective proof of responses to the stimuli. The responses to the stimuli are analyzed by means of methods of signal processing and then objectively checked for their existence with the aid of a detection test.

[0012] In one advantageous embodiments [sic] of the invention, the light source emitting the optical stimulation is controlled such that graduated light intensities can be differentiated by physiological sensory perception. The result is amplified, digitized, and the put into an evaluation system, whereby appropriate evaluation logarithms are utilized in order to create the objective sensitivity profile of the visual field.

[0013] A subject is preferably shown a spatial pattern generated by at least two light impulses on a screen, whereby the sequence of light intensity of the impulses shown corresponds to a platinum sequence. The subject's potential responses are recorded with the aid of an EEG or MEG or an ERG measuring system, and upon analysis of these potential responses a conclusion is drawn regarding the functionality of the impulse localizations tested. The results can be used to topographically depict the functionality of the visual system.

[0014] The significant advantage of the method according to the invention lies in the fact that it is possible to determine the sensitivity profile of the visual field—as is common in static perimeters. This was not the case with the methods known heretofore. This way, a direct comparison of subjective and objective perimeter exam results can be made for the first time. The subjective perception of the light impulses presented can be assessed objectively using EEG/MEG and/or ERG analysis. Since the new process is completely automated, the strain on the patient is extremely low. Another advantage is noticeably higher of the functional diagnostic reliability arising from the elimination of patient error and errors made by the examining physician.

[0015] The object of the invention is further an apparatus for performing the above-mentioned method, with which apparatus a planar or a curved screen is positioned in the visual field of the subject and upon which screen optical impulses with a defined chronological intensity sequence are generated at predetermined positions, preferably by means of light sources that have been arranged in a perimeter.

[0016] The light intensity as well as the chronological sequence of the light impulse produced by the light sources can be adjusted adequately throughout the area of physiological interest. Preferable light sources are light emitting diodes.

[0017] Because of the sequence of light intensity corresponding to the platinum sequence, such an impulse modus presents to the subject a random spatial and time pattern for the visual system that is independent from the number of active light sources. Since the visual system can recognize neither a regular spatial pattern, nor a regular time pattern, adaptation—such as has been known from the past impulse sequences—an be eliminated. Thus possible acclimatization to the impulse and the resulting decrease in attention can be counteracted.

[0018] The basis for creating a platinum sequence is an m-sequence (MLS—Maximum Length Sequence) s₁(n) of the length N. From this m-sequence, a second m-sequence s₂(n) is created through decimation. In doing so, the periodically repeated initial sequence of each value is taken, where d and N must be relative prime. The calculation is done in accordance with the following rule:

s ₂(n)=s ₁(dn), where d=2^(k)+1

[0019] and k such that r (order of sequence, N=2^(r−)1), divided by the largest common divisor of r and k, is odd and natural. By multiplying the two sequences by element, random product sequences

s(n)=s ₁(n)*s ₂(n +u)

[0020] can be formed and be summarized with the initial sequences as a family of M=N+2 sequences. Here the following applies:

s ₀(n)∈{s ₁(n),s ₂(n),s ₁(n)*s ₂(n+u)}where 0≦u<N

[0021] The significant advantage compared to stimulation sequences used so far is that new information is constantly being given to the visual system by means of the intentional exclusion of subjectively perceptible patterns. This causes the readiness to perceive to constantly be maintained at a high level, and the examined physiological values have higher intensities than with the conventional methods.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Below, the invention is described in greater detail using the drawings as a guideline. In that,

[0023]FIG. 1 depicts a modular mimic display of the measuring position for the determination of the visual system's sensitivity profile;

[0024]FIG. 2 depicts the example of an implemented platinum sequence.

DETAILED DESCRIPTION OF THE DRAWINGS

[0025]FIG. 1 depicts a symbolic patient sitting in front of a spherical projection screen such as a perimeter 1 in which light impulses of adequate intensity are generated at defined locations either by means of active light sources (LED—light emitting diodes) or using a projection system by means of a calibrated light source.

[0026] These light sources are controlled by a control system 2, such as a PC with an appropriate software program, in such a way that the chronological sequence of intensity of the emitted light corresponds to the requirements of the signal theory and the physiology of perception of the generation requirement for platinum sequences (see FIG. 2). Such an optical impulse causes changes—also referred to as impulse responses—in the EEG/MEG. These responses are recorded, intensified, and digitized by an appropriate apparatus 3 that may comprise an ERG/EEG measuring system and an AD converter. The digitized impulse responses are processed and analyzed in the control system 2.

[0027] As long as the LEDs light up individually, it is possible to subjectively answer the question as to whether or not they are seen by the patient if the patient cooperates. In order to significantly shorten the examination time, the LEDs are not controlled individually, but simultaneously. This kind of stimulation is referred to as multifocal stimulation. Here, a subjective evaluation of the responses to the impulses is no longer possible, and the control system 2 takes over the evaluation. Since it is known during evaluation in what sequence the individual impulse positions were triggered, each stimulation response belonging to each stimulation position can be calculated from the overall potential cortical and retinal responses. 

We claim:
 1. Method for optical stimulation of the visual system during a perimeter exam, characterized in that graduated light intensities are used for the optical stimulation of the visual system; the chronological sequence and spatial pattern of the light impulses are determined depending on the proof of impulse responses, and the existence of impulse responses is checked and analyzed by means of signal processing methods.
 2. Method according to claim 1, characterized in that the light source or sources are controlled such that graduated light intensities can be differentiated by physiological sensory perception.
 3. Method according to claims 1 or 2, characterized in that the enhanced EEG is digitized and sent to an evaluation system.
 4. Method according to any of claims 1 through 3, characterized in that the objective sensitivity profile of the visual field is determined with the use of appropriate evaluation logarithms.
 5. Method for the automated functionality exam of the visual system, characterized in that a spatial pattern consisting of at least two light impulses are shown to a subject on a screen; the light intensity is varied sequentially, where the sequence of the light intensity of the stimuli shown corresponds to a platinum sequence; the subject's potential responses are recorded by means of an EEG or MEG or an ERG measuring system; and, the evaluation of the potential responses provide information regarding the functionality of the stimulus localizations tested.
 6. Apparatus for performing a method according to any of the above claims, whereby a subject is shown a pattern, characterized in that a planar or curved screen is positioned in the subject's field of vision, on which screen optical impulses are generated at pre-determined locations by means of light sources.
 7. Apparatus according to claim 6, characterized in that the light sources are arranged in a perimeter (1) and the responses to the stimuli are amplified and digitized by a device (3) that preferably includes an ERG/EEG measuring system and an AD converter, where the device (3) is connected to a PC loaded with an evaluation software for the purpose of performing an evaluation, and the light sources are connected to a PC loaded with control software.
 8. Apparatus according to claim 7, characterized in that the light sources are light emitting diodes. 